Microwave hybrid junction



Dec. 22, 1959 s. B. COHN MICROWAVE HYBRID JUNCTION Filed Dec; 1, 1954 ATTORNEY United States Patent MICROWAVE HYBRID JUNCTION Seymour B. Cohn, Palo Alto, Calif., assignor to Sperry Rand Corporation, a corporation of Delaware Application December 1, 1954, Serial No. 472,475

6 Claims. (Cl. 333-11) This invention relates to a microwave energy coupling device, and more particularly, is concerned with a microwave coupler having the properties of a hybrid junction.

It has heretofore been proposed to provide apparatus for coupling energy propagating in the dominant mode in a rectangular wave guide into a circular wave guide wherein the energy so coupled propagates in the circular wave guide in a circularly polarized mode. This may be accomplished, for example, by coupling an end of the circular wave guide to the broad wall of a rectangular wave guide by means of suitable coupling means. See the copending application Serial No. 234,125 filed June 28, 1951, now US. Patent No. 2,723,377 dated November 8, 1955, in the name of the inventor of the present application. It has been found, in accordance with the principles of the present invention, that by providing suitable means coupled to the circular wave guide, a device having the properties of a hybrid junction is effected. This requires coupling means that not only couples energy between the TE mode in the rectangular wave guide to the circularly polarized TE mode in a circular wave guide, but requires that the coupling means be such as to eifect 100 percent power transfer between the two wave guide sections, and further requires mutual- 1y exclusive propagation means for splitting the energy propagating in the circular wave guide into two equal components which propagate in the dominant mode in two respective rectangular wave guides.

It is therefore a general object of this invention to provide a novel hybrid junction type microwave coupler.

-Another object of this invention is to provide for splittingequally between two output terminals substantially 100 percent of the energy coupled into one terminal of a four terminal network.

Another object of the invention is to provide a novel four terminal microwave device wherein energy coupled into any one of the terminals will divide equally between two other terminals with no energy being propagated to a fourth terminal.

These and other objects of the invention which will become apparent as the description proceeds are achieved by providing apparatus including a first wave guide of rectangular cross-section for propagating microwave energy of the TE mode, and a circular wave guide section which is connected at rightangles to one of the broad walls of the rectangular wave guide section for propagating energy in the circularly polarized TE i mode. Coupling means, including a pair of slots in the broad Wall of the rectangular wave guide section within the region bounded by the circular wave guide section, which slots are resonant at the operating frequency of the device, provide 100 percent power coupling of the energy propagated in the one direction in the rectangular wave guide section to the circular wave guide section. The slots are oriented to couple the longitudinal and transverse currents respectively in the rectangular wave guide section. Second and third rectangular wave guide sections are coupled to the circular wave guide section at right angles to each other and at right angles to the longitudinal axis of the circular wave guide. The planes of the broad walls of the second and third wave guides are perpendicular to the plane of the broadwall of the first rectangular wave guide. i

For a better understanding of the invention, reference should be had to the accompanying drawing, whereinz Fig. 1 is a perspective view showing the preferred form of the hybrid junction of the present invention;

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1;

Figs. Sa-d are diagrams used in explaining of the operation of the present invention; and

Figs. 4a-d are diagrams used in explaining another aspect of the operation of the present invention.

Referring to the preferred embodiment of Figs. land 2, the numeral 10 indicates generally a section of rectangular wave guide designed to propagate energy in the TE mode at a design frequency of f Joined at right angles to one of the broad walls of the rectangular wave guide 10 is a section of circular wave guide 12, the two wave guide sections being joined so that their longitudinal axes intersect at right angles to each other. Coupling is provided between the two wave guide sections by means of a pair of resonant slots 14 and 16. The slot 14 extends in a direction transverse'to the axis of the wave guide 10 with its center positioned substantially along the longitudinal axis of the circular wave guide 12. The slot 16 is positioned parallel to and adjacent one of the narrow walls of the rectangular waveguide section 10 and to one side of the slot 14, the slot 16 having its center substantially along the longitudinal axis of the slot 14 to form a T-configuration, as shown.

With the slot 14 providing coupling to the longitudinal electric currents in the wave guide section 10 and with the slot 16 providing coupling to the transverse currents in the wave guide 10, it has been found that two waves are launched in the circular wave guide 12, each propagated in the TE mode, with their electric vectors in time and spacequadrature. By definition, such waves, providing they are equal in amplitude, may be considered components of a single circularly polarized wave. i

As illustrated in the diagrams of Fig. 3, the direction of propagation in the rectangular wave guide 10 determines the direction of rotationof the circularly polarized wave in the circluar wave guide 12. Thus, as shown in Fig. 3a, if energy is propagated from the left toward the junction, the resulting electric field vector of the wave in the circular wave guide rotates in a clockwise motion viewed from behind. If, as shown in Fig. 3b, energy is propagated in the wave guide 10 from right to left toward the junction, the circularly polarized wave in the wave guide 12 rotates in a counterclockwise direction. Similarly, as shown in Figs. 3c and 3d, circularly polarized energy, depending upon the direction of rotation thereof, launches energy either to the right or to the left of the junction in the rectangular wave guide 10.

As mentioned above, one of the important aspectsof the present invention is the provision of a coupler which acts as a hybrid junction, which by definition isa fourterminal-pair network with equal power splitting between two output terminals and no power coupling out the third terminal. By proportioning the slots 14 and 16 to couple percent of the power from the rectangular wave guide 10 intothe circular wave guide 12, such a hybrid junction can be achieved by arranging suitable output terminals for coupling to the respective components of the circularly polarized wave in the circular wave guide 12. As an example, two output rectangular wave guide sections 18 and 20, having their longitudinal axes peipendicular to the longitudinalaxis of the circular one aspect Patented Dec. 22, 1959 wave guide section 12 as. well as perpendicular to each other, are provided. Each of the rectangular wave guide sections 18 and 20 is arranged with the broad Walls thereofparallel to the longitudinal axis of the circular wave guide section 12.

Any circularly'or elliptically polarized wave may be resolved into two linearly-polarized mutually-perpendicular components. These components may be arbitrarily represented by the vectors E and E in Fig. 1. It may be seen that vector E is correctly oriented to couple to wave guide 18, and vector E is correctly oriented to couple to wave guide 20. It is to be understood that so far as the present invention is concerned the angular orientation of wave guides 18 and 20 with respect tothe longitudinalaxis of circular wave guide 12, as illustrated in Fig. 1, 'is purely arbitrary, and they may have substantially any angular orientation -solong as their longitudinal axes remain disposed at right angles to each other,

Thus, assuming 100 percent power transfer by the coupling slots 14 and d6, energy propagated in one direction down the rectangular wave guide section 10 splits equally between the two output rectangular wave guide sections 18 and 20 with none of the energy being propagated beyond the junction point down the wave guide section 10. Likewise, energy coupled into either of the rectangular wave guide sections 18 and 20 divides'equal- 1y at the junction and propagates in both directions along therectangular wave guide section 10 but no energy is coupled to the other of the rectangular wave guide sections 18 or 20. A four-terminal junction is therefore provided which has the properties of a hybrid junction. It has been foundthat the coupling slots 14 and 16 effect 100 percent power transfer when their lengths are such that they are resonant at the operating frequency f that is, when their lengths are equal to substantially a half wave length. A short circuiting wall 22 is provided at a location that gives the best match between the re spcctive modes in the circular wave guide 12 and the rectangular wave guides 18 and 20. Additional matchtug means (not shown) such'as irises may also be in corporated to create a perfect refiectionless match.

I The hybrid characteristics of the above-described coupler are illustrated in Figs. 4a and b. A wave of normalized amplitude /2 approaching the junction from either the right or the left results in two orthogonal linearly polarized wavesin the circular wave guide of normalized amplitude 1 which are 90 out of phase a circularly polarized wave, the relative phase depending upon the direction in which the wave is propagated in the rectangular wave guide. Similarly, as shown in 'Figs. 4c and d, a' linearly polarized wave of normalized amplitude /2 propagated in the circular wave guide splits the junction into two equal waves traveling in opposite directions having a normalized amplitude of 1.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above'description or shownin the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A hybrid junction comprising a first section of hollow rectangular wave guide having apair of broad walls joined along their longitudinal edges by a pair of narrow walls, ais ectionof icircular wave guide having its longitudinalaxis intersecting the longitudinal axis of the rectangular wave guide at right angles, the circular-wave guide being joined at one end to one of thebroad'walls of ;the'; rectangular wave guide and" being *short-circuited at the other end, said oneof the broad'walls of the rectangular wave guide having first and-second elongated slots-"therein spaced-apart in the regionbounded-by -the circular wave guide, the firstslot extending substantially in a direction perpendicular to the longitudinal axis of the rectangular wave guide and the second slot extending substantially in a direction parallel to the longitudinal axis of the rectangular wave guide, the first slot being positioned with the center thereof located at the point of intersection between the longitudinal axis of the circular wave guide and said one of the broad walls of the rectangular wave guide, the second slot being positioned with the center thereof in a common plane with the center of the first slot, said plane being transverse to the longitudinal axis of the rectangular wave guide, the second slot further being positioned to one side adjacent one of the narrow walls of the rectangular wave guide, both of the slots being substantially a half wave length long at the operating frequency of the hybrid junction, whereby the slots couple all of the energy in one waveguide section to the other wave guide section,- and second and third hollow rectangular wave guide sections coupled respectively at one of their ends tothe circular waveguide, the longitudinal axes of said second and third wave guides extending at right angles to each other and to the longitudinal axis of the circular wave guide, the broad walls of said second and third wave guides lying in planes which are parallel to the longitudinal axis of said circular waveguide.

2. A hybrid junction for coupling microwave energy comprising a first rectangular wave guide adapted for conveying ultrahigh frequency energy of the TE mode, means including a section of waveguide having a circular cross section open on one end and closed on theother end with said open end joined to one of the broad walls of said first rectangular wave guide with the longitudinal axis of said circular wave guide extending perpendicular to the longitudinal axis of 'said first rectangular'wav'e guide, means for intercoupling said two wave guides for converting substantially all'the energy of .the TE mode in said first rectangular wave guide into energy of Ithe TE circularly polarized mode "in said circular wave guide, said intercoupling means including two elongated openings spaced-apart and'disposed in the common wall separating said rectangular wave guide-from said circular wave guide, one of said elongated openings extending in a direction perpendiculartothe longitudinal axisofisaid rectangular wave guide'and theother ofsaidelongated openings disposed substantially parallel toiand adjacent to one of the narrow walls of said'rectangular wave guide, and second :and'third hollow rectangular wave guide sections joined respectively-at one of theiriends to the wall of 'said circular'wave' guide for coupling respectively to components of energy-intheicircular wave'guide having their electric vectors in space quadrature, said second and third rectangular wave guideshavingtheir longitudinal axes perpendicular to the longitudinal :axis of said circular wave guide and the planes of the-broad wallsrof said second and third rectangular wave guides being perpendicular to the'plane of said one broad wall of said first rectangular wave guide.

3. A hybrid junction as in claim 2 wherein'both of said elongated openings are substantially a halfwave length long at the operating frequency of the hybrid junction whereby said elongated openingsicouplefiall of the energy from said first rectangular wave guide section into said circular wave guide section.

4. A four-terminal wave guide network having .the properties of a hybrid junction comprising a first rectaugular wave guide adapted for conveying ultra :high'frcquency energyof the 'TE' mode, arsection .of-xcircular waveguide joined at one end to one broad wall .of-said first rectangular wave guide so that the longitudinal-axes of said two waveguides intersect each other at right angles said one broad wall 'ofsa'id rectangular wave guide -having first and second elongated slots therein spaced-apart ina I -configuration in the'region bounded by the --circi rlar wave guide for-intercoupling said Y two wave guides and converting all of the energy of the T13 mode in said first rectangular wave guide into energy of and said broad wall of said first rectangular wave guide and the second slot longitudinally disposed adjacent to one of the narrow walls of said first rectangular wave guide and extending substantially in a direction parallel to the longitudinal axis of said first rectangular wave guide with the center thereof in a common plane with the center of the first slot, said plane being transverse to the longitudinal axis of said first rectangular wave guide, both of said slots being dimensioned to be substantially resonant at the operating frequency of said network, and second and third rectangular wave guide sections spaced in quadrature with each other and joined respectively at one of their ends to the wall of said circular wave guide so that the longitudinal axes of said second and third rectangular wave guide sections are perpendicular to the longitudinal axis of the circular wave guide and the planes of the broad walls of said second and third rectangular wave guide sections are normal to the plane of said broad wall of said first rectangular wave guide section, and means for short circuiting the other end of said circular wave guide to give the best match between the respective modes in the circular wave guide and said second and third rectangular wave guides, whereby said second and third rectangular wave guide sections couple respectively to components of energy linearly polarized in mutually perpendicular planes within said circular wave guide.

5. A hybrid junction for coupling microwave energy comprising a first rectangular wave guide adapted to propagate microwave energy in the TE mode, a section of circular wave guide having its longitudinal axis intersecting the longitudinal axis of the rectangular wave guide at right angles, the circular wave guide being joined at one end to one of the broad walls of said rectangular wave guide and being short-circuited at the other end, coupling means resonant at the frequency of waves propagating in said hybrid junction for providing substantially 100 percent transfer of energy between said two wave guides, said coupling means causing energy propagating in one direction in said first rectangular wave guide to couple into said circular wave guide and propogate therein in a circularly polar ized TE mode, and second and third hollow rectangular wave guide sections coupled respectively at one of their ends to the circular wave guide, the longitudinal axes of said second and third wave guides extending at right angles to each other and to the longitudinal axis of the circular wave guide, and the broad walls of said second and third wave guides lying in planes which are parallel to the longitudinal axis of said circular wave guide.

6. A hybrid junction for coupling microwave energy comprising a first rectangular wave guide section adapted to propagate microwave energy in the TE mode, a section of circular wave guide open on one end and closed on the other end with said open end joined to one of the broad walls of said rectangular wave guide with the longitudinal axis of said circular wave guide section extending perpendicular to the longitudinal axis of said rectangular wave guide, means for coupling substantially all of the energy propagating in one direction in the rectangular wave guide into the circular wave guide, said coupling means launching circularly polarized energy into the circular wave guide from energy propagating in the TE mode in one direction in the rectangular wave guide, and first and second microwave transmission means coupled to said circular wave guide for coupling: two substantially equal magnitude microwave energy components from said circular wave guide, said first and second transmission means being disposed at right angles to each other and to the longitudinal axis of said circular wave guide and together being adapted to couple substantially all the circularly polarized energy from said circular wave guide.

References Cited in the file of this patent UNITED STATES PATENTS 2,412,320 Carter Dec. 10, 1946 2,573,746 Watson Nov. 6, 1951 2,714,707 Zabel Aug. 2, 1955 2,723,377 Cohn Nov. 8, 1955 2,759,099 Olive Aug. 14, 1956 2,867,773 Korman Jan. 6, 1959 FOREIGN PATENTS 592,224 Great Britain Sept. 11, 1947 OTHER REFERENCES Article by Watson, Resonant Slots, pub. in the Journal of The Institution of Electrical Engineers, vol. 93, part 3A, No. 4, pages 758-762, 1946. 

